PHAGOCYTOSIS: At the Crossroads of Innate and Adaptive Immunity

Abstract

Phagocytosis, the process by which cells engulf large particles, requires a substantial contribution of membranes. Recent studies have revealed that intracellular compartments, including endocytic organelles and the endoplasmic reticulum (ER), can engage in fusion events with the plasma membrane at the sites of nascent phagosomes. The finding that ER proteins are delivered to phagosomes, where degraded peptides are loaded onto major histocompatibility complex (MHC) class II molecules, has significantly enhanced our understanding of the immune functions associated with these organelles. Although it is well known that pathogens are killed in phagosomes, the contribution of ER proteins to phagosomes has provided a novel pathway for the loading of exogenous peptides onto MHC class I molecules, a process known as cross-presentation. Thus, phagocytosis has evolved from a nutritional function in unicellular organisms to play key roles in both innate and adaptive immunity in vertebrates.

A summer heat wave decreases the immunocompetence of the mesograzer, Idotea baltica

“…The immune system of invertebrates can be divided into cellular and humoral defences. Phagocytosis represents the most important feature of cellular immunity (Jutras and Desjardins 2005). During phagocytosis, reactive oxygen species are produced with a high antimicrobial potential (Bachere et al 1995).…”

High‐resolution quantitative proteome analysis reveals substantial differences between phagosomes of RAW 264.7 and bone marrow derived macrophages

“…Phagocytosis is induced through the binding of particles to cell surface receptors such as the mannose receptor, Fc‐receptors, or scavenger receptors. After internalization, newly formed phagosomes engage in a maturation process that involves fusion with endosomes, lysosomes, and other organelles 7, 8 leading to the formation of phagolysosomes in which the foreign matter is degraded. Peptide antigens from the particle are also presented via MHC class I and II molecules, bridging innate and adaptive immunity.…”

Phagocytosis of neonatal pathogens by peripheral blood neutrophils and monocytes from newborn preterm and term infants

“…Although primarily an innate immune process, degradation and processing of microbes during phagocytosis for presentation via major histocompatibility complexes is also a crucial link to adaptive immune system responses (1). Individuals with phagocytic defects (e.g., Wiskott-Aldrich syndrome (2)) are at an increased risk of bacterial infection.…”

“…The formation of the phagosome around an ingested entity during phagocytosis relies on low pH for bactericidal functions and antigen processing and presentation (1,18). pHrodo is a highly pH-sensitive succinimidyl ester dye that fluoresces dramatically when exposed to low pH (<4.0).…”